Looking at the works of Banū Mūsā in comparison with the Greek tradition one cannot only detect a forward leap in the variation of techniques in their engineering designs, but can also detect their participation in the general cultural mood of early Islamic times that was critical of the Greek scientific tradition. However, when their works are compared to the work of Jazarī we note a remarkable maturity in the latter's work that is nowhere to be found in the works of Banū Mūsā. With Jazarī we begin to notice discussions regarding the real function of mechanical devices, and real appreciation of their significance as tools that did not only fulfill daily functions for the society, but that they were also tools that could demonstrate the way in which the natural physical principles worked.[377] His devices were examples of natural physical principles in action. And in the introduction to his book, he explicitly states that his devices were intended to actualize (ikhrāj min al-quwwa ilā al-f'l)[378] — the physical principles that were potentially there, waiting to be actualized. His full grasp of the Aristotelian approach to mechanical devices and their intrusion into the world of nature is far superior to Banū Mūsā's understanding of such principles as far as one can tell from their surviving writings.
Even the historical sources preserve for us anecdotes about the patrons of Banū Mūsā, especially al-Mutawakkil (ruled 847-861), and tell us that Banū Mūsā's devices had indeed enchanted him,[379] and that those skillful engineers produced for him such entertaining objects exactly to serve that very purpose. Contrast that with the patron of Jazarī who demanded of him, according to Jazarī's own introduction to his work, that Jazarī should compose the work in order to keep a record of the peerless "models" (ashkāl), things that he invented (istanbaṭa), and "illustrations" (mithālāt) that he brought forth. For anyone reading that introduction, the language reveals very clearly a fuller understanding of how mechanical devices operated and why they did. At times Jazarī would even explicitly state that he intended to illustrate the same principle with many devices, all in order to show the universal applications of those principles.
But as these texts have not been fully studied from those perspectives yet, one has to wait before passing any more detailed judgments about them regarding their relative merits. The impressions given here resulted from a first quick reading of the sources, and will, I am sure, finally withstand the test of analysis.
Or take the works of Ibn al-Nafīs in medicine. It was in his commentary on Avicenna's Canon that we find his remarkable remark that did not only depart from the teachings of Avicenna, whom he admired greatly, but went further to criticize Avicenna's original source, Galen himself. With his criticism, he ended up refuting the doctrines of Galen on the basis of his own observations, and thus laid the foundation for the eventual discovery of the pulmonary circulation of the blood.[380] It was in the post-Ghazālī period that such scientists seem to have gained a well-earned confidence in order to challenge their predecessors and through them attack the main Greek legacy that continued to be the site of contention, with such statements as "this is the common opinion, but according to us, it is false" (hādha huwa al-ra'y al-mashhūr, wa-huwa 'indana bāṭil). These are echoes of Ibn al-Haitham, 'Urḍī, Ṭūsī, and others who said, at one point or another, "This is the accepted opinion, but according to us it is false." In that regard, Ibn al-Nafīs reflects the same trend that was developing in astronomy, and had already had its roots in the works of al-Rāzī some four centuries before him. He also seemed to have been complementing the works of other scientists from other disciplines who were all engaged in a cultural revival rather than an age of decline.
Consider also the work of Kamāl al-Dīn al-Fārisī (d. 1320)[381] from the following century, which illustrates the same trend again, but from the field of optics. It was al-Fārisī's teacher, the great astronomer Quṭb al-Dīn al-Shīrāzī (d. 1311), who suggested to al-Fārisī that he study the work of the great scientist Ibn al-Haitham (d.c.1038) from the pre-Ghazālī period. Note that he was not advised to go as far back as the obsolete Greek optics for his study. Instead he was put to challenge the best and most recent production on the subject.
Neither the Greek tradition, nor Ibn al-Haitham had managed to explain the phenomenon of the rainbow properly, and thus up till al-Fārisī's time this problem had remained the site of competition and speculation. And it was al-Fārisī who finally put his mind to it, and developed the instrumentation in order to explain how the colors of the rainbow were in fact produced. And exactly like his predecessor, Ibn al-Nafīs, he too followed the same style, that is, he produced an elaborate commentary on the most advanced work of a pre-Ghazālī scientist. And in the context of that commentary he refuted the ideas of his predecessor and the ideas of the more ancient Greeks who had nevertheless been his models to some extent. In this regard, it should be remembered that although Ibn al-Haitham could be counted as a great scientist in his own right, he too did not hesitate to reject Greek ideas when they did not meet his exacting scientific standards. And yet it was al-Fārisī who had the final say in the matter of the rainbow.
In a sense,, this phenomenon is very similar to what took place in astronomy. Here too we find the formidable critique of Ptolemaic astronomy, which was leveled by Ibn al-Haitham in the middle of the eleventh century. We also find the same critique left as such, without anything more positive being done about it till the thirteenth century, when the astronomer Mu'ayyad al-Dīn al-'Urḍī (d. 1266), who lived more than a century after Ghazālī, complained against Ibn al-Haitham for not bringing anything new besides criticism. It was 'Urḍī who undertook the development of a whole alternative astronomy that was destined to replace the Greek astronomy, and thereby produced his famous mathematical theorem that made its impact on almost all astronomers that followed him. Here again there is no comparison between the brilliance of 'Urḍī and that of Ibn al-Haitham, startling and brilliant as Ibn al-Haitham was.
Still, in the discipline of astronomy this trend continued after 'Urḍī, through Ṭūsī, Quṭb al-Dīn al-Shīrāzī (d. 1311), Niẓām al-Dīn al-Nīsābūrī (d. 1328), Ibn al-Shāṭir (1375) and his contemporary Ṣadr al-Sharī'a al-Bukhārī (c. 1350), ''Alā al-Dīn al-Qushjī (d. 1474), Mullā Fatḥallāh al-Shirwānī (c. 1450), and finally to Shams al-Dīn al-Khafrī (d. 1550) to name only a few. Each and every one of those astronomers would take the works that were produced in the pre-Ghazālī period, and refer to them as the commonly known astronomy (al-mashhūr) only to attack them severely, and attack Ptolemy behind them as well. After having done that, they would then go on to build their own alternatives to that astronomy on grounds that were completely new, and on levels that were much more sophisticated than the levels found in the earlier period or the Greek sources themselves.
379
See
380
Ibn al-Nafīs, Abū al-Ḥasan 'Alā al-Dīn b. Abī al-Ḥazm al-Qarshī al-Dimashqī (d. 1288),